Signing up is simple and only took two taps to login via Facebook and start a 48 free-trial of Spotify Premium on my iPhone. Once the trial ends the service reverts to Spotify Free which gives ad-supported streaming access to a catalogue of some 16 million songs. Unfortunetly Spotify Free only gives access via a Mac or PC and streaming to an iPhone or iPad requires a $12.99 monthly subscription to Spotify Premium.
A quick flick through the catalogue had all the tracks I wanted available to play instantly and audio-quality was great via wi-fi. Using the in-app Settings I bumped the stream quality to High (160kbit/s) and turned on a 5 second crossfade to avoid the iTunes match style buffering gap between songs. The app uses 20-50MB of data per hour of streaming music so make sure you’ve got a good data plan or connected to wi-fi before hitting play.